The long-term objective of this revised proposal is the development of tissue engineering strategies that will promote the constructive remodeling and vascularization of scaffolds used for tissue and organ reconstruction. The present four-year proposal would utilize xenogeneic extracellular matrix (ECM) derived from porcine urinary bladder (UB-ECM) as the test scaffold material and two animal models of esophageal reconstruction as the preclinical in vivo test system. Three important issues concerning the mechanisms of scaffold remodeling will be studied: 1) the source of cells that contribute to the remodeling process, 2) the temporal and spatial association of scaffold degradation with vascularization and tissue reconstruction, and 3) the concept of seeding and culturing cells within scaffolds in vitro to promote subsequent in vivo vascularization and remodeling. There are four Specific Aims, each of which is addressed by a controlled, carefully designed study. The first Specific Aim will examine the concept of host bone marrow-derived cells as a source of multi-potential cells for scaffold remodeling. This Aim will also examine the effect of protein cross-linking upon the source of cells that populate these scaffolds. The second Specific Aim will determine the rate of ECM scaffold degradation, the fate of degradation products, and the association of scaffold degradation with the remodeling process. The third and fourth Specific Aims will investigate the effect upon scaffold remodeling of culturing vascular mural precursor cells or marrow-derived endothelial precursor cells, respectively, within the ECM scaffold prior to in vivo implantation. All studies are based upon extensive preliminary data and upon clearly stated hypotheses. The studies are directed toward understanding the mechanisms of scaffold remodeling and applying the learned principles to broader tissue engineering applications. The work will be conducted by an experienced interdisciplinary team of scientists and a timeline is presented for completion of the work.